For example, a vehicle drive apparatus for a railway vehicle, a railway rolling stock, and the like includes a plurality of main electric motors respectively arranged on a bogie in proximity to wheels and control devices for driving these main motors. The main motor is connected to the wheels via gears, and the main motor rotates the wheels, whereby the entire rolling stock runs. The main electric motor receives electric power via wires from the control device arranged under a floor of the rolling stock, and the operation of the main motor is controlled by the control device. Therefore, a set of a main motor and a control device is deemed as one drive apparatus. When the main motor and the control device are integrally arranged or arranged in proximity to each other, it is not necessary to route long wires, in which case an ideal drive apparatus can be achieved.
Recently, the control device is mainly arranged in a different position away from the main motor, such as a position under a floor of a central portion of the rolling stock. One of the reasons therefor is a volume occupied for cooling. The control device generates heat due to switching of devices when the rolling stock accelerates and decelerates. Recently, it is common to use a method for cooling the control device by using the natural wind generating by the traveling of the rolling stock. The amount of the wind due to the traveling of the rolling stock increases as the velocity of the rolling stock increases, but in general, the wind is as low as about 2 to 4 m/s. Therefore, the control device is provided with many radiating fins in order to increase the area of heat radiation, and also uses heat pipes in order to expedite the heat radiation. The volume of the portion needed for cooling occupies 60% or more of the entire control device. Therefore, the control device for the railway vehicle is different from control devices for automobiles and generators and is large in volume. Thus, it is difficult to integrally form the control device with the main motor within the bogie, whose size is strictly limited.
In order to reduce the size of the control device, it is conceivable to reduce the volume of the radiating fins occupying more than half of the volume of the control device. For example, the volume needed for heat radiation may be reduced by using a forced air cooling. However, when a cooling fan for the forced air cooling is attached, a stop of the cooling fan due to malfunction and the like may result in insufficient cooling effect. As a result, the device will break down, and the vehicles will stop. Therefore, the cooling device requiring electric power increases the risk of the malfunction.
Accordingly, it is conceivable to forcibly cool the control device by blowing cooling wind into a cooling device by using the rotation of the main motor. An example of the drive apparatus using the above method and integrally formed with the main motor and the main control device is an apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2007-37262. In this apparatus, a fan arranged on a rotor of a main motor rotates according to rotation of the main motor, and the fan draws fresh air. The drawn fresh air passes through the control device. At this occasion, the air removes heat from the control device, and the air is discharged to the outside. Since the fans reliably rotate whenever the main motor rotates, a malfunction of the cooling fan alone will never occur.
However, the above-explained conventional vehicle drive apparatus has the following problem to be solved. That is, in the drive apparatus for the railway vehicle, the main motors are arranged on the bogie, which produces extremely strong vibration. When the control device is integrally formed with the main motor, the control device directly receives the vibration from the bogie and the main motor. Although the motors do not break down because the motors are designed to withstand the vibration of the bogie, the currently available control device may break down since it is not sufficiently designed to be vibration-proof.